Racism:
1 :a belief that race is the primary determinant of human traits and capacities and that racial differences produce an inherent superiority of a particular race
2 :racial prejudice or discrimination
So yeah, if E had said, "I hate that Captain America is black now." or "Iron Man is fighting that black guy." That would be racist (and offensive.)
But he didn't say anything like that. He said ,
In other words,
"The history of the US involves a civil war that was largely tied up with racism and slavery, so Marvel should have thought of that before they promoted their civil war comic with a big picture of different races fighting. It's pretty funny that they didn't think of that!"
How is that racist?